JP2015038219A - Single crystal for scintillator, heat treatment method for producing single crystal for scintillator and method of producing single crystal for scintillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a single crystal for scintillators which can reduce sufficiently the fluorescence output difference between on the cerium low-concentration side and on the cerium high-concentration side, a heat treatment method for production of the single crystal and a production method for the single crystal.SOLUTION: A single crystal for scintillators contains a cerium-activated orthosilicate compound of formula (1): GdLnLuCeLmSiO, where Lm is at least one element selected from Pr, Tb and Tm; Ln is at least one element selected from lanthanoid elements other than Pr, Tb and Tm and Sc and Y; 'a' is a value smaller than 1; x is a value larger than 1 and smaller than 2; y is a value larger than 0 and 0.01 or smaller; z is a value larger than z and 0.01 or smaller; and a+x+y+z is 2 or smaller.

Description

  The present invention relates to radiation such as gamma rays in fields such as radiology, physics, physiology, chemistry, mineralogy, and petroleum exploration for medical diagnosis positron CT (PET), cosmic ray observation, underground resource search, etc. The present invention relates to a scintillator single crystal used in a single crystal scintillation detector (scintillator), a heat treatment method for producing a scintillator single crystal, and a method for producing a scintillator single crystal. The present invention relates to a scintillator single crystal containing an orthosilicate compound, a heat treatment method for producing a scintillator single crystal, and a method for producing a scintillator single crystal.

  An orthosilicate gadolinium compound scintillator using cerium as an activator has been put to practical use as a radiation detector such as positron CT (hereinafter referred to as PET) because of its short fluorescence decay time and large radiation absorption coefficient. However, although such a scintillator has a fluorescence output larger than that of the BGO scintillator, it is only about 20% of the NaI (Tl) scintillator, and its improvement is desired.

A scintillator using a single crystal of cerium-activated lutetium orthosilicate represented by the general formula Lu _{2 (1-x)} Ce _2x SiO ₅ (see, for example, Patent Documents 1 and 2), a general formula Gd _{2− (x + y)} Ln use _x Ce _y SiO ₅ (Ln is that Sc, Tb, Dy, Ho, Er, Tm, Yb and at least one element selected from the group consisting of Lu) and cerium-activated orthosilicate lutetium gadolinium single crystal represented by Scintillators (see, for example, Patent Documents 3 and 4) and cerium represented by the general formula Ce _2x (Lu _1-y Y _y ) SiO ₅ Ce _2x (Lu _1-y Y _y ) _{2 (1-x)} SiO ₅ A scintillator using a single crystal of activated lutetium yttrium silicate (see, for example, Patent Documents 5 and 6) is known. In these scintillators, it is known that not only the crystal density is improved, but also the fluorescence output of the single crystal of the cerium activated orthosilicate compound is improved and the fluorescence decay time can be shortened.

Ln _{2− (x + y)} Lu _x Ce _y SiO ₅ (Ln includes Y and is represented by at least one element selected from the group consisting of Sc, Tb, Dy, Ho, Er, Tm, Yb, and Lu) It is known that single crystals of cerium-activated lutetium orthosilicate have scintillators with different fluorescence decay times by changing the cerium concentration of the activator.

  In recent years, with the development of PET, the development of next-generation high-performance PET that combines scintillators with different fluorescence decay times is expected. The fluorescence output is high, the energy resolution is excellent, and the difference in fluorescence output is small. A small scintillator is required.

  However, when the cerium concentration of the activator is changed, there is a problem that not only the fluorescence decay time changes, but also the fluorescence output and energy resolution are lowered, resulting in variations in scintillator characteristics.

  In addition to the cerium concentration, the cause of the characteristic variation is considered to be oxygen deficiency in the crystal lattice. The generation of oxygen vacancies forms an energy trap level, which increases the background of fluorescence output (afterglow) due to thermal excitation from the level and increases the variation in fluorescence output. It is done.

General formula: Ce _2x Ln _2y Lu _{2 (1-xy)} SiO ₅ (wherein Ln is at least one element of lanthanoid elements excluding Lu, and 2 × 10 ⁻⁴ ≦ x ≦ As a cerium-activated lanthanoid silicate scintillator single crystal represented by 3 × 10 ⁻² , 1 × 10 ⁻⁴ ≦ y ≦ 1 × 10 ⁻³ ), a co-activated lutetium silicate single crystal of Ce and Tm is a patent document. 7 describes that the variation in the ingot vertical position of the fluorescence output, decay time, and energy resolution is improved.

General _{formula: (Ln 1-x1-x2} -x3 Ln 'x1 Ce x2 Tb x3) 9.33 (SiO 4) 6 O 2 ( wherein, Ln and Ln' are different from each other, La, Gd, and Yb, and Lu X ₁ , x ₂ and x ₃ are represented by 0 <x ₁ <1, 0 <x ₂ <0.05, 0 <x ₃ <0.05, 0 <x ₂ + x ₃ <0.1, 0 <x ₁ + x ₂ + x ₃ <1) A scintillator characterized by being composed of a lanthanide silicic acid single crystal is described in Patent Document 8, and a known oxyorthosilicate It is described that it is a scintillator that obtains good performance as compared to that obtained using

Japanese Patent No. 2852944 U.S. Pat. No. 4,958,080 Japanese Examined Patent Publication No. 7-78215 US Pat. No. 5,264,154 US Pat. No. 6,624,420 US Pat. No. 6,921,901 JP 2006-199727 A Japanese Patent Laid-Open No. 2-64008

  A DOI (Depth of Interaction) type next-generation high-performance PET in which scintillators having different fluorescence decay times are combined is required to have a specific decay time difference and a small difference in fluorescence output and energy resolution. In the cerium-activated lutetium orthosilicate compound single crystal, the fluorescence decay time can be adjusted by changing the cerium concentration in the raw material, and application to a high-performance DOI-type PET scintillator is being studied. However, since the fluorescence output decreases on the cerium low concentration side where the fluorescence decay time is short, the output difference from the scintillator with a long combination fluorescence decay time becomes a problem in discriminating the energy spectrum. Therefore, in the cerium activated lutetium orthosilicate compound, it is required to reduce the cerium concentration dependence of the fluorescence output.

  In addition, although patent document 7 describes the effect that the characteristic variation of the upper part and the lower part of the crystal in the ingot is 15% or less, there is no description about the characteristic difference between ingots having different cerium concentrations in the raw material.

  The first invention of the present invention has been made in view of the above-mentioned problems of the prior art, and provides a scintillator single crystal capable of sufficiently reducing the difference in fluorescence output between the low concentration side and the high concentration side of cerium. The purpose is to do. Further, the first invention provides a heat treatment method for manufacturing a scintillator single crystal capable of sufficiently reducing a difference in fluorescence output between a cerium low concentration side and a high concentration side, and a method for manufacturing the scintillator single crystal. The purpose is to provide.

  The second invention of the present invention has been made in view of the above-mentioned problems of the prior art, and the fluorescence decay time is long enough to facilitate the difference in fluorescence decay time between the two types of scintillators to be combined to 10 ns or more. An object is to provide a scintillator single crystal and a method for producing the same.

1st invention provides the single crystal for scintillators containing the cerium activated orthosilicate compound represented by following General formula (1).
_{Gd 2- (a + x + y} + z) Ln a Lu x Ce y Lm z SiO 5 ...... (1)
(In General Formula (1), Lm represents at least one element selected from Pr, Tb and Tm, Ln represents at least one element selected from Sc, Y, and a lanthanoid element excluding Pr, Tb and Tm. Represents an element, a represents a value of 0 or more and less than 1, x represents a value greater than 1 and less than 2, y represents a value greater than 0 and less than or equal to 0.01, and z is greater than 0 and less than or equal to 0.01 (The value of a + x + y + z is 2 or less.)

  According to the single crystal for scintillator of the first aspect of the present invention, it has a configuration including the cerium activated orthosilicate compound represented by the general formula (1), so that the difference in fluorescence output between the low concentration side and the high concentration side is obtained. Can be sufficiently reduced. According to the single crystal for scintillator of the present invention, by adding at least one element selected from Pr, Tb and Tm to the single crystal of the cerium-activated orthosilicate compound and co-activating with cerium In particular, the fluorescence output and energy resolution on the cerium low concentration side can be improved, and the difference in fluorescence output and energy resolution between the cerium low concentration side and the high concentration side can be sufficiently reduced.

  In the scintillator single crystal of the first invention, the Ln is Gd, the a is greater than 0 and less than 1, and the Lm is at least one element selected from Tb and Tm. preferable. On the other hand, when the concentration of Pr is higher than an appropriate amount, the fluorescence wavelength is detected on the short wavelength side by interacting with Gd, so that the degree of improvement in fluorescence output and energy resolution is reduced as a scintillator single crystal. Tend to.

  In the single crystal for a scintillator according to the first aspect of the present invention, the Ln is Y, and the value a is preferably greater than 0 and less than 1. When Ln is Y, since the distortion of the crystal structure of the host structure LSO is small, fluorescence output and energy resolution can be improved.

  In the single crystal for a scintillator according to the first aspect of the invention, the Ln is Y, the a is preferably greater than 0 and less than or equal to 0.2, and the x is preferably greater than 1.6 and less than 2. . When Ln is Y and the values of a and x are in the above ranges, the distortion of the crystal structure of the host structure LSO is small, so that the fluorescence output and energy resolution can be improved.

  The single crystal for scintillator according to the first aspect of the present invention includes at least one additive element selected from elements belonging to Group 2 (Group IIa) of the periodic table, from 0.00005 to 0.1 mass based on the total mass of the single crystal. % Content is preferable. In this case, a decrease or variation in fluorescence characteristics that may be caused by oxygen defects is reduced, thereby improving the fluorescence characteristics of the single crystal and reducing afterglow caused by crystal defects that become the background of fluorescence output. To do.

  The single crystal for scintillator according to the first aspect of the present invention comprises at least one additive element selected from elements belonging to Group 13 (Group IIIb) of the periodic table, and 0.00005 to 0.1 mass based on the total mass of the single crystal. % Content is preferable. In this case, the fluorescence characteristics of the single crystal are improved, and the effect of reducing afterglow due to crystal defects that becomes the background of the fluorescence output becomes more remarkable. Furthermore, a higher effect can be obtained by being present simultaneously with one or more additive elements selected from the elements belonging to Group 2 of the periodic table.

Moreover, 1st invention is the heat processing method for manufacturing the single crystal for scintillators, Comprising: The element of the scintillator single crystal containing the cerium activated orthosilicate compound represented by following General formula (1) is shown. Provided is a heat treatment method in which a single crystal grown using a contained raw material is heat treated at a temperature of 700 to 1500 ° C. in an atmosphere containing oxygen.
_{Gd 2- (a + x + y} + z) Ln a Lu x Ce y Lm z SiO 5 ...... (1)
(In General Formula (1), Lm represents at least one element selected from Pr, Tb and Tm, Ln represents at least one element selected from Sc, Y, and a lanthanoid element excluding Pr, Tb and Tm. Represents an element, a represents a value of 0 or more and less than 1, x represents a value greater than 1 and less than 2, y represents a value greater than 0 and less than or equal to 0.01, and z is greater than 0 and less than or equal to 0.01 (The value of a + x + y + z is 2 or less.)

  According to this heat treatment method, variation in element distribution in a single crystal (single crystal ingot) due to segregation between elements is reduced, and afterglow characteristics and characteristic deterioration that may be caused by oxygen defects are reduced. It is possible to provide a scintillator single crystal capable of sufficiently reducing the difference in fluorescence output between the low concentration side and the high concentration side of cerium. In addition, according to the present heat treatment method, it is possible to provide a scintillator single crystal in which the fluorescence output and energy resolution on the cerium low concentration side with a particularly short decay time are improved.

Moreover, 1st invention is a manufacturing method of the single crystal for scintillators, Comprising: The raw material containing the constituent element of the single crystal for scintillators containing the cerium activated orthosilicate compound represented by following General formula (1) A method for producing a scintillator single crystal, comprising the steps of preparing and growing a single crystal by the Czochralski method and heat-treating the single crystal at a temperature of 700 to 1500 ° C. in an atmosphere containing oxygen I will provide a.
_{Gd 2- (a + x + y} + z) Ln a Lu x Ce y Lm z SiO 5 ...... (1)
(In General Formula (1), Lm represents at least one element selected from Pr, Tb and Tm, Ln represents at least one element selected from Sc, Y, and a lanthanoid element excluding Pr, Tb and Tm. Represents an element, a represents a value of 0 or more and less than 1, x represents a value greater than 1 and less than 2, y represents a value greater than 0 and less than or equal to 0.01, and z is greater than 0 and less than or equal to 0.01 (The value of a + x + y + z is 2 or less.)

  This manufacturing method not only reduces defects and cracks during crystal growth due to segregation between elements, improves fluorescence characteristics, but also reduces afterglow characteristics and characteristic degradation that may be caused by oxygen defects. It is possible to provide a method for producing a scintillator single crystal capable of sufficiently reducing the difference in fluorescence output between the low concentration side and the high concentration side. Moreover, according to this manufacturing method, the manufacturing method of the single crystal for scintillators which the fluorescence output and energy resolution of the cerium low concentration side with especially short decay time improved can be provided.

A second invention is a scintillator single crystal containing a cerium-activated orthosilicate compound represented by the following general formula (2), and is at least one selected from elements belonging to Group 2 (Group IIa) of the periodic table The additive element is contained in an amount of 0.00005 to 0.1% by mass based on the total mass of the single crystal, and the ratio of the fluorescence intensity at the excitation wavelength of 364 nm to the fluorescence intensity at the excitation wavelength of 304 nm (364 nm) at the fluorescence wavelength of 420 nm. A single crystal for a scintillator having a / 304 nm) of less than 3.
_{Gd 2- (a + x + y} + z) Ln a Lu x Ce y Lm z SiO 5 ...... (2)
(In general formula (2), Lm represents at least one element selected from Pr, Tb and Tm, Ln represents at least one element selected from Sc, Y, and a lanthanoid element excluding Pr, Tb and Tm. Represents an element, a represents a value of 0 or more and less than 1, x represents a value of more than 1 and less than 2, y represents a value of more than 0.01 and 0.03 or less, and z is 0 or more and 0.01 (The following values are shown, where a + x + y + z is 2 or less.)

  According to the single crystal for scintillator of the second aspect of the invention, having a configuration including the cerium activated orthosilicate compound represented by the general formula (2), the difference in fluorescence decay time between two types of scintillators to be combined is 10 ns or more. It is possible to obtain a fluorescence decay time that is long enough to facilitate the above.

The second invention is a method for producing a scintillator single crystal, comprising a raw material containing a constituent element of a scintillator single crystal containing a cerium-activated orthosilicate compound represented by the following general formula (2): Provided is a method for producing a scintillator single crystal, comprising the steps of preparing and growing a single crystal by the Czochralski method.
_{Gd 2- (a + x + y} + z) Ln a Lu x Ce y Lm z SiO 5 ...... (2)
(In General Formula (1), Lm represents at least one element selected from Pr, Tb and Tm, Ln represents at least one element selected from Sc, Y, and a lanthanoid element excluding Pr, Tb and Tm. Represents an element, a represents a value of 0 or more and less than 1, x represents a value of more than 1 and less than 2, y represents a value of more than 0.01 and 0.03 or less, and z is 0 or more and 0.01 (The following values are shown, where a + x + y + z is 2 or less.)

  According to this production method, it is possible to produce a scintillator single crystal having a long fluorescence decay time to such an extent that the difference in fluorescence decay time between two types of scintillators to be combined is easily set to 10 ns or more.

  According to the first invention, it is possible to provide a scintillator single crystal that can sufficiently reduce the difference in fluorescence output between the low concentration side and the high concentration side. In addition, according to the first invention, it is possible to provide a scintillator single crystal with improved fluorescence output and energy resolution particularly on the cerium low concentration side with a short decay time. In addition, according to the first invention, a heat treatment method for producing a scintillator single crystal capable of sufficiently reducing the difference in fluorescence output between the cerium low concentration side and the high concentration side, and production of the scintillator single crystal A method can be provided.

  According to the second aspect of the present invention, it is possible to provide a scintillator single crystal having a long fluorescence decay time and a method for manufacturing the same so that the difference in fluorescence decay time between the two types of scintillators to be combined is easily set to 10 ns or more.

It is a schematic cross section which shows an example of the basic composition of the growth apparatus used for the growth of the single crystal for scintillators of the 1st and 2nd invention. It is a fluorescence spectrum in the excitation wavelength of 364 nm of the single crystal for scintillators obtained by the Example and the comparative example. Each spectrum is displayed with a maximum output value of 1. It is an excitation wavelength spectrum in the fluorescence wavelength 420nm of the single crystal for scintillators obtained by the Example and the comparative example.

  Hereinafter, preferred embodiments of the present invention will be described in detail. In the following description, one of the preferred embodiments of the first invention is referred to as “first embodiment”, and one of the preferred embodiments of the second invention is referred to as “second embodiment”. .

The scintillator single crystal of the first embodiment includes a cerium-activated orthosilicate compound represented by the following general formula (1).
_{Gd 2- (a + x + y} + z) Ln a Lu x Ce y Lm z SiO 5 ...... (1)
(In General Formula (1), Lm represents at least one element selected from Pr, Tb and Tm, Ln represents at least one element selected from Sc, Y, and a lanthanoid element excluding Pr, Tb and Tm. Represents an element, a represents a value of 0 or more and less than 1, x represents a value greater than 1 and less than 2, y represents a value greater than 0 and less than or equal to 0.01, and z is greater than 0 and less than or equal to 0.01 (The value of a + x + y + z is 2 or less.)

Here, when the value of a + x + y + z in the general formula (1) is 2, the general formula (1) is represented by the following general formula (3).
_{Ln 2- (x + y + z} ) Lu x Ce y Lm z SiO 5 ...... (3)
(In General Formula (3), Ln represents a lanthanoid element including Lu, excluding Pr, Tb and Tm, and at least one element selected from Sc and Y, and Lm is at least selected from Pr, Tb and Tm. 1 represents one element, x represents a value greater than 1 and less than 2, y represents a value greater than 0 and less than or equal to 0.01, and z represents a value greater than 0 and less than or equal to 0.01, where x + y + z Is less than or equal to 2.)

  In the scintillator single crystal containing the cerium-activated orthosilicate compound represented by the general formula (3), since x, y and z in the general formula (3) are within the above ranges, Thus, a fluorescence output with a short fluorescence decay time can be obtained.

  In general formula (3), the larger the value of x, the higher the density of crystals and the higher the fluorescence output at room temperature. Therefore, the value of x needs to be more than 1 and less than 2, preferably 1.2 or more and less than 2, more preferably 1.4 or more and less than 2, more preferably 1.6 or more and 2 More preferably, it is less than.

  In the general formula (3), the value of y needs to be more than 0 and 0.01 or less, preferably 0.00005 or more and 0.01 or less, and 0.0001 or more and 0.01 or less. Is more preferably 0.0002 or more and 0.005 or less, and most preferably 0.0005 or more and 0.003 or less. If y is 0, sufficient fluorescence output cannot be obtained, and if it exceeds 0.01, crystal coloring becomes remarkable in the heat treatment step including oxygen after growth, which causes a problem of reduction in fluorescence output.

  In the general formula (3), the value of z needs to be greater than 0 and less than or equal to 0.01, preferably greater than 0 and less than 0.01, and is 0.0001 or more and 0.005 or less. More preferably, it is 0.0001 or more and 0.004 or less, and most preferably 0.0002 or more and 0.001 or less. If z is 0, the fluorescence output is reduced, and if it exceeds 0.01, the coloration of the crystal becomes remarkable, and the reduction of the fluorescence output and the occurrence of cracks due to crystal distortion become a problem.

  On the other hand, when the value of a + x + y + z in the general formula (1) is less than 2, Gd is an essential element. Also in this case, since the single crystal for scintillator has a, x, y, and z in the above general formula (1) within the above ranges, a fluorescence output with a short fluorescence decay time can be obtained at room temperature.

  When the value of a + x + y + z is less than 2, a in general formula (1) is preferably 0 or more and 0.5 or less, more preferably more than 0 and 0.5 or less, more than 0 and more than 0. It is more preferably 4 or less, particularly preferably more than 0 and 0.2 or less, and most preferably more than 0.05 and 0.2 or less. When a exceeds 0.5, the crystal structure is distorted, and the occurrence of cracks in the crystal tends to increase. Further, when a is 0, it is difficult to suppress Gd segregation, which may cause a decrease in fluorescence characteristics.

  Moreover, the preferable range of the value of x, y, z in the said General formula (1) is respectively the same as the preferable range of the value of x, y, z in the said General formula (3).

The scintillator single crystal of the second embodiment includes a cerium-activated orthosilicate compound represented by the following general formula (2).
_{Gd 2- (a + x + y} + z) Ln a Lu x Ce y Lm z SiO 5 ...... (2)
(In general formula (2), Lm represents at least one element selected from Pr, Tb and Tm, Ln represents at least one element selected from Sc, Y, and a lanthanoid element excluding Pr, Tb and Tm. Represents an element, a represents a value of 0 or more and less than 1, x represents a value of more than 1 and less than 2, y represents a value of more than 0.01 and 0.03 or less, and z is 0 or more and 0.01 (The following values are shown, where a + x + y + z is 2 or less.)

  In the scintillator single crystal represented by the general formula (2), a, x, y, and z in the general formula (2) are within the above ranges, respectively, so that the fluorescence property at room temperature is excellent, In particular, it is possible to obtain excellent characteristics in combination with a semiconductor detector such as an avalanche photodiode that has excellent sensitivity to light having a long wavelength of 500 nm or longer.

  In the general formula (2), the value of y needs to be more than 0.01 and 0.03 or less, preferably more than 0.01 and less than 0.03, more than 0.01 and less than 0. Is more preferably 0.012 or more and 0.02 or less, and most preferably 0.012 or more and 0.018 or less. If y is 0.01 or less, a sufficient fluorescence output cannot be obtained with a semiconductor detector excellent in sensitivity to a fluorescence wavelength of 500 nm or more, and if it exceeds 0.03, coloration of crystals after growth becomes remarkable. There arises a problem that the output is reduced and the number of crystal cracks is increased.

  In the general formula (2), the value of z needs to be 0 or more and 0.01 or less, preferably 0 or more and less than 0.01, and 0.0001 or more and 0.005 or less. Is more preferably 0.0001 or more and 0.004 or less, and most preferably 0.0001 or more and 0.001 or less. If the ratio of the fluorescence intensity at the excitation wavelength of 364 nm to the fluorescence intensity at the excitation wavelength of 304 nm (364 nm / 304 nm) is less than 3 at the fluorescence wavelength of 420 nm where the fluorescence output is almost the maximum even when z is 0, the fluorescence output is obtained. There is no problem, and if it exceeds 0.01, the coloration of the crystal becomes remarkable, and the decrease in fluorescence output and the occurrence of cracks due to crystal distortion become a problem.

  Moreover, the preferable range of the value of a and x in the said General formula (2) is the preferable range of the value of a and x in the said General formula (1) from the reason similar to the case of the said General formula (1). Are the same.

  In the general formulas (1), (2) and (3), Ln is a lanthanoid element excluding Pr, Tb and Tm, and at least one element selected from Sc and Y. More preferably, a lanthanoid element having an ionic radius larger than Dy and not more than Lu, and at least one element selected from Sc and Y are selected. When the matrix structure is LGSO, the lower part of the ingot is obscured due to the influence of segregation of Gd, and the fluorescence characteristics tend to deteriorate. However, the lanthanoid elements and Sc that are relatively close to Lu or smaller than Lu are used. By containing at least one element selected from Y, the segregation of Gd is suppressed, the dust at the lower part of the ingot is eliminated, and the deterioration of the fluorescence characteristics is suppressed. Among these contained elements, Sc, Y, and Yb are more preferable because single crystal growth is relatively easy even if they are present in a large amount in the crystal, and an effect can be obtained without deteriorating the fluorescence characteristics, thereby improving the fluorescence characteristics. Y is most preferable in that it can be made to occur.

  The scintillator single crystal of the first embodiment preferably contains at least one additive element selected from elements belonging to Group 2 (Group IIa) of the periodic table. As a result, it is possible to reduce a decrease or variation in fluorescence characteristics that may be caused by oxygen defects, and it is possible to reduce the background (afterglow) of fluorescence output caused by crystal defects. The content of this additive element is preferably 0.00005 to 0.1% by mass, based on the total mass of the scintillator single crystal, since the above effect can be obtained more sufficiently. It is more preferable that it is 0.02 mass%. As the element to be contained, one or more elements selected from Ca and Mg are preferable among the elements belonging to Group 2 (IIa group) of the periodic table because the above-described effects can be more sufficiently obtained.

The single crystal for scintillator according to the second embodiment has at least one additive element selected from elements belonging to Group 2 (IIa group) of the periodic table, based on the total mass of the scintillator single crystal, 0.00005-0. .1% by mass is contained. As a result, it is possible to reduce a decrease or variation in fluorescence characteristics that may be caused by oxygen defects, and it is possible to reduce the background (afterglow) of fluorescence output caused by crystal defects. In addition, as an effect of containing an element belonging to Group 2 (IIa group) of the periodic table, crystal coloring and fluorescence output due to a change in Ce valence (Ce ³⁺ ⇒ Ce ⁴⁺ ) due to a trace amount of oxygen in the growth atmosphere during crystal growth The decrease can be suppressed. This effect tends to become prominent when the Ce concentration is high, and it has also been found that the valence change of Ce (Ce ³⁺ ⇒ Ce ⁴⁺ ) forms crystal defects similar to oxygen defects. An effect of further reducing the output background (afterglow) can be obtained. The content of the additive element needs to be 0.00005 to 0.1% by mass, based on the total mass of the scintillator single crystal, since the above effect can be obtained more sufficiently. It is preferable that it is 005-0.02 mass%. As the element to be contained, one or more elements selected from Ca and Mg are preferable among the elements belonging to Group 2 (IIa group) of the periodic table because the above-described effects can be more sufficiently obtained.

  In addition, the scintillator single crystals of the first and second embodiments preferably contain at least one additive element selected from elements belonging to Group 13 (IIIb group) of the periodic table. As a result, the effect of reducing the background (afterglow) of the fluorescence output that seems to be caused by crystal defects becomes even more remarkable. The content of this additive element is preferably 0.00005 to 0.1% by mass, based on the total mass of the scintillator single crystal, since the above effect can be obtained more sufficiently. It is more preferable that it is 0.02 mass%. Further, when the additive element is present at the same time as one or more additive elements selected from Ca and Mg among the elements belonging to Group 2 (Group IIa) of the periodic table, a higher effect may be obtained. . As the element to be contained, one or more elements selected from Al, Ga, and In are preferable among the elements belonging to Group 13 (Group IIIb) of the periodic table because the above-described effects can be more sufficiently obtained.

  Further, in the scintillator single crystals of the first and second embodiments, the total concentration of one or more elements selected from elements belonging to Groups 4, 5, 6 and 14, 15, 16 of the periodic table is set. The total mass of the scintillator single crystal of the first or second embodiment is preferably 0.002% by weight or less. Thereby, deterioration of fluorescence characteristics can be suppressed.

  The scintillator single crystal containing the cerium-activated orthosilicate compound represented by the above general formulas (1) and (3) of the first embodiment has an excitation wavelength of 304 nm at a fluorescence wavelength of 420 nm at which the fluorescence output is substantially maximum. The ratio of the fluorescence intensity at the excitation wavelength of 364 nm to the fluorescence intensity at 364 nm (364 nm / 304 nm) is preferably 10 or more, more preferably 20 or more, and most preferably 30 or more. Thereby, the effect of further speeding up the fluorescence decay time can be obtained while maintaining a high fluorescence output.

  On the other hand, the scintillator single crystal containing the cerium-activated orthosilicate compound represented by the general formula (2) of the second embodiment has an excitation wavelength of 304 nm at a fluorescence wavelength of 420 nm at which the fluorescence output is almost maximum. The ratio of the fluorescence intensity at the excitation wavelength of 364 nm to the fluorescence intensity (364 nm / 304 nm) is less than 3, and preferably less than 2. As a result, although the fluorescence decay time is slightly delayed, the long wavelength component in the vicinity of 500 nm of the fluorescence wavelength increases, and the energy conversion efficiency of the semiconductor photodetector having the highest sensitivity above 500 nm such as an avalanche photodiode is increased. Can be improved.

  Moreover, the scintillator single crystal of the first embodiment uses a raw material containing the constituent elements of the scintillator single crystal including the cerium-activated orthosilicate compound represented by the general formulas (1) and (3). The single crystal grown in this manner is preferably manufactured through a process of heating in an oxygen-containing atmosphere (hereinafter referred to as “heat treatment process”). By passing through the heat treatment step, variation in fluorescence output due to the occurrence of oxygen vacancies can be reduced. That is, oxygen deficiency can be sufficiently reduced without changing the trivalent cerium ion to tetravalent by heat-treating the single crystal at a lower temperature in an atmosphere containing oxygen. As a result, the single crystal that has undergone such a heat treatment method has a more excellent fluorescence characteristic because the background (afterglow) is reduced without lowering the fluorescence output and the variation in fluorescence output can be suppressed. Can be realized.

  The atmosphere containing oxygen preferably has an oxygen concentration of 1 volume% or more and 100 volume% or less, and is an atmosphere containing nitrogen or an inert gas (for example, an air atmosphere). Among them, an atmosphere having an oxygen concentration of 30% by volume or more is more preferable, and an atmosphere having an oxygen concentration of 50% by volume or more is particularly preferable. When the oxygen concentration is less than 1% by volume, the oxygen partial pressure is low, and oxygen hardly diffuses into the crystal, so that the above-described effect according to the first embodiment is hardly obtained. Since a higher oxygen concentration is desirable, a method of circulating oxygen at a constant flow rate using a closed furnace is also effective.

  The heating temperature of the single crystal in the heat treatment step is 700 ° C to 1500 ° C, and preferably 1000 ° C to 1300 ° C. If the heating temperature is less than 700 ° C., the above-described effect according to the first embodiment tends to be difficult to obtain. If the heating temperature is higher than 1500 ° C., the cerium ions are likely to change to tetravalent, causing the single crystal to be colored and It becomes a factor which makes it fall.

  The above-mentioned heat treatment method is applied to a single crystal grown using a raw material containing a constituent element of a single crystal for scintillator including a cerium activated orthosilicate compound represented by the general formulas (1) and (3) Thus, it is possible to suppress the generation of oxygen vacancies as much as possible, reduce the background (afterglow), and maximize the fluorescence output and energy resolution.

  In contrast, in the production of the scintillator single crystal of the second embodiment, a raw material containing a constituent element of the scintillator single crystal containing the cerium-activated orthosilicate compound represented by the general formula (2) is used. When the single crystal grown in this way is heated in an oxygen-containing atmosphere, the action of changing trivalent cerium ions to tetravalent becomes prominent, thereby deteriorating fluorescence characteristics. Sometimes. Therefore, the “heat treatment step” is not suitable for the second embodiment.

  Next, an example of the manufacturing method of the scintillator single crystal of 1st and 2nd embodiment is demonstrated.

  In the method for producing a scintillator single crystal according to the first and second embodiments, first, a raw material of the cerium-activated orthosilicate compound represented by the general formula (1) or (2) is given a predetermined stoichiometric composition. Mix the mixture into a crucible. As a starting material for producing this single crystal, Gd, Lu which are constituent elements of a cerium-activated orthosilicate compound with at least one selected from praseodymium, terbium and thulium represented by the general formula (1) Si, Pr, Tb, Tm, Ce single oxide and / or composite oxide is preferably used. As a commercially available product, it is preferable to use a product having high purity such as that manufactured by Shin-Etsu Chemical Co., Ltd., Stanford Material Co., Ltd., Tama Chemical Co., Ltd., or Japan Yttrium Co.

  In addition, when the single crystal contains an element belonging to Group 2 of the periodic table (Group IIa) and / or an element belonging to Group 13 of the periodic table (Group IIIb), the timing of adding these additional elements is as follows: If it is before the growth of a crystal | crystallization, it will not specifically limit. For example, an additive element may be added and mixed when the raw material is weighed, and when the raw material is added to the crucible, it belongs to the periodic table group 2 (IIa group) and / or the periodic table group 13 (IIIb group). Elements may be mixed. Moreover, the aspect at the time of addition will not be specifically limited if an additive element is contained in the grown single crystal, For example, you may add in a raw material in the state of an oxide or carbonate.

  Next, the crucible filled with the above raw material is heated to melt the raw material (melting step), and then the molten liquid is cooled and solidified (cooling and solidifying step) to obtain a single crystal ingot.

  Here, the Czochralski method may be adopted as the melting method in the above melting step, or another method may be adopted. When performing the melting step by the Czochralski method, it is preferable to perform operations in the melting step and the cooling and solidifying step using the pulling apparatus 10 having the configuration shown in FIG.

  FIG. 1 is a schematic cross-sectional view showing an example of a basic configuration of a growth apparatus for growing a single crystal in the manufacturing methods according to the first and second embodiments. A pulling apparatus 10 shown in FIG. 1 has a high-frequency induction heating furnace 14. This high frequency induction heating furnace 14 is for continuously performing the operations in the melting step and the cooling and solidification step described above.

  The high-frequency induction heating furnace 14 is a bottomed container having a cylindrical side wall having fire resistance, and the shape of the bottomed container itself is the same as that used for single crystal growth based on the known Czochralski method. A high frequency induction coil 15 is wound around the side surface of the bottom of the high frequency induction heating furnace 14. A crucible 17 (for example, an Ir crucible) is disposed on the bottom surface inside the high-frequency induction heating furnace 14. This crucible 17 also serves as a high-frequency induction heater. When a single crystal raw material is put into the crucible 17 and high frequency induction is applied to the high frequency induction coil 15, the crucible 17 is heated to obtain a melt 18 (melt) made of a single crystal constituent material.

  In addition, an opening (not shown) penetrating from the inside of the high frequency induction heating furnace 14 to the outside is provided at the center of the bottom of the high frequency induction heating furnace 14. A crucible support bar 16 is inserted from the outside of the high-frequency induction heating furnace 14 through this opening, and the tip of the crucible support bar 16 is connected to the bottom of the crucible 17. By rotating the crucible support rod 16, the crucible 17 can be rotated in the high-frequency induction heating furnace 14. A space between the opening and the crucible support rod 16 is sealed with packing or the like.

  Next, a more specific manufacturing method using the pulling device 10 will be described.

  First, in the melting step, a single crystal raw material is put into the crucible 17 and high frequency induction is applied to the high frequency induction coil 15 to obtain a melt 18 (melt) made of a single crystal constituent material.

  Next, the columnar single crystal ingot 1 is obtained by cooling and solidifying the melt in the cooling and solidifying step. More specifically, the work proceeds in two steps, a crystal growth step and a cooling step described later.

  First, in the crystal growth process, the pulling rod 12 with the seed crystal 2 fixed to the lower end is introduced into the melt 18 from the upper part of the high frequency induction heating furnace 14, and then the single crystal ingot 1 is lifted while pulling the pulling rod 12. Form. At this time, in the crystal growth step, the heating output of the heater 13 is adjusted, and the single crystal ingot 1 pulled up from the melt 18 is grown until the cross section has a predetermined diameter.

  Next, in the cooling step, the heating output of the heater is adjusted to cool the grown single crystal ingot obtained after the crystal growth step.

  In the manufacturing methods according to the first and second embodiments, it is preferable that the atmosphere for crystal growth contains oxygen in the range of 0 to 0.6% by volume. When the oxygen concentration exceeds 0.6% by volume, the fluorescence output may decrease due to coloring or the like. Further, when an iridium crucible is used, evaporation loss due to oxidation of the iridium crucible becomes a problem.

  In the manufacturing method according to the first embodiment, the single crystal is heat-treated in an oxygen-containing atmosphere after the growth or after the growth / processing (heat treatment step). The effect of increasing the fluorescence output can be obtained due to the reduction of coloring due to the heat treatment. As the heat treatment temperature, a temperature of 700 ° C. to 1500 ° C. at which the above effect is easily obtained is applied.

  In the manufacturing method according to the first embodiment, this single crystal is co-activated with cerium by adding praseodymium, terbium, or thulium to the single crystal of the cerium-activated orthosilicate compound, preferably further By containing an element belonging to Group 2 (Group IIa) of the periodic table and / or an element belonging to Group 13 (Group IIIb) of the periodic table, the fluorescence output and energy resolution are improved, and the difference in fluorescence output due to the difference in cerium concentration Can be used as a scintillator in which Each of these addition amounts is adjusted so that the content in the manufactured scintillator single crystal becomes the content in the scintillator single crystal of the first embodiment.

  In the manufacturing method according to the second embodiment, it is not essential that the single crystal is co-activated with cerium by adding praseodymium, terbium, or thulium to the single crystal of the cerium-activated orthosilicate compound. It is essential to add an element belonging to Group 2 (Group IIa) of the periodic table. Each of these addition amounts is adjusted so that the content in the manufactured scintillator single crystal becomes the content in the scintillator single crystal of the second embodiment.

  Therefore, this single crystal is used for medical diagnosis positron CT (PET), cosmic ray observation, underground resource search, etc. for radiology, physics, physiology, chemistry, mineralogy, and oil exploration. It is very useful as a single crystal for a scintillator used in a single crystal scintillation detector (scintillator) for radiation of a large amount of radiation, and is particularly effective for next-generation high performance PET combining scintillators with different decay times.

  The preferred embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example at all.

[Example 1]
<Production of single crystal>
Single crystals were produced by the Czochralski method. First, the stoichiometry of _Ln as a starting material _{2- (x + y + z)} Lu x Ce y Lm z SiO 5 (Ln = Lu, Lm = Pr, x = 1.996, y = 0.003, z = 0.001) So as to be a composition, lutetium oxide (Lu ₂ O ₃ , purity 99.99 mass%), silicon dioxide (SiO ₂ , purity 99.9999 mass%), cerium oxide (CeO ₂ , purity 99.99 mass%), Praseodymium oxide (Pr ₆ O ₁₁ , purity 99.99% by mass) was mixed to obtain a mixture of 500 g in total. In addition, 0.087748 g of calcium carbonate (CaCO ₃ , purity 99.99% by mass) (corresponding to 0.007% by mass as Ca) was weighed.

  Next, 500 g of the obtained raw material mixture and the weighed calcium carbonate were put into an iridium crucible having a diameter of 50 mm, a height of 50 mm and a thickness of 1.5 mm, and heated to a melting point of about 2100 ° C. in a high frequency induction heating furnace. The melt was obtained. In addition, melting | fusing point was measured with the electronic optical pyrometer (Chiano Co., Ltd. make, Pyrosta MODEL UR-U).

Subsequently, seeding was performed by putting the tip of a pulling rod having a seed crystal fixed to the tip into the melt. Thereafter, the shoulder of the single crystal ingot was pulled up at a crystal pulling speed of 1.5 mm / h, and when the diameter became 25 mm (φ), the growth of the parallel part was started at a pulling speed of 1 mm / h. After growing a crystal having a predetermined weight, the single crystal was separated from the melt, and cooling was started. When growing the crystals, 4 L / min of N ₂ was kept flowing in the growth furnace. At this time, the oxygen concentration in the growth furnace was less than 0.02% by volume. Thus, a single crystal ingot having a crystal weight of 280 g, a shoulder portion of 30 mm, and a parallel portion of 90 mm was obtained. About the obtained single crystal ingot, the result of the segregation coefficient of Pr 0.36, the segregation coefficient 0.22 of Ce, and the segregation coefficient 0.15 of Ca was obtained from the result of the elemental analysis. The segregation coefficient is represented by the general formula (4).
Cs / Co = k (1-g) ^k-1 (4)
(Co: solute concentration in the melt, Cs: concentration in the crystal, k: effective segregation coefficient, g: solidification rate)

A sample of 4 × 6 × 20 mm ³ was cut out from the upper part of the single crystal ingot thus obtained, arbitrarily extracted five crystal samples, placed on a platinum plate, and put into an electric furnace. The temperature in the electric furnace was increased over about 3 to 4 hours in the air atmosphere, held at 1200 ° C. for 12 hours, and then cooled to room temperature over about 5 to 8 hours. Next, the crystal sample was subjected to chemical etching using phosphoric acid, and the entire surface of the crystal sample was mirror-finished. This obtained the single crystal for scintillators of Example 1.

<Measurement of fluorescence characteristics>
The remaining five except for one of the four surfaces of the 4 × 6 × 20 mm ³ scintillator single crystal (each sample) having a size of 4 mm × 6 mm (hereinafter referred to as “radiation incident surface”). The surface was coated with polytetrafluoroethylene (PTFE) tape as a reflective material. Next, optical grease is applied to the photomultiplier surface (photoelectric conversion surface) of a photomultiplier tube (trade name “H7195”, manufactured by Hamamatsu Photonics Co., Ltd.) on the radiation incident surface that is not coated with the PTFE tape of each sample obtained. Fixed. Next, each sample was irradiated with 662 keV gamma rays using ¹³⁷ Cs, the energy spectrum of each sample was measured, and the fluorescence output and energy resolution of each sample were evaluated. The energy spectrum is obtained by applying a signal of 1.45 kV to the photomultiplier tube and converting the signal from the dynode into a preamplifier (ORTEC, product name “113”) and a waveform shaping amplifier (ORTEC, product name “ 570 ") and measured with MCA (trade name" Quantum MCA4000 "manufactured by PGT). The fluorescence decay time is obtained by inputting a signal from the anode of the photomultiplier tube to a digital oscilloscope (trade name “TDS5052”, manufactured by Tektronix) with an input impedance of 50Ω and averaging the signal 10,000 times. It was calculated from the fluorescence decay curve. Table 1 shows the composition formula of this example and the measurement results of the fluorescence characteristics (fluorescence output, energy resolution, fluorescence decay time) as an average value of each sample.

  In addition, ultraviolet excitation fluorescence characteristics were measured using a spectrofluorometer (Hitachi F-4500), excitation wavelength 200 to 400 nm, fluorescence wavelength 200 to 700 nm, sampling interval 4 nm, scan speed 1200 nm / min, excitation and fluorescence side. The measurement was performed under the conditions of a slit of 2.5 nm and a PMT (photomal) voltage of 400 V. Calculate the ratio (364 nm / 304 nm) of the fluorescence intensity at 364 nm, which is the main excitation wavelength, to the fluorescence intensity at 304 nm, which is the main excitation wavelength, at a fluorescence wavelength of 420 nm where the fluorescence output is almost maximum, The values are shown in Table 1.

  In addition, the excitation wavelength spectrum about wavelength 420nm is shown in FIG. In FIG. 3, D2 indicates Example 1, and A2, B2, C2, E2, and F2 indicate Example 13, Example 14, Example 15, Comparative Example 4, and Comparative Example 7, which will be described later.

[Example 2]
Examples except that the amounts of lutetium oxide and cerium oxide as starting materials were adjusted so that x = 1.996 was x = 1.985 and y = 0.003 was y = 0.0005 In the same manner as in Example 1, a scintillator single crystal of Example 2 was produced. Further, the obtained single crystal for scintillator was measured for fluorescence characteristics in the same procedure as in Example 1. Table 1 shows the composition formula of this example and the measurement results of the fluorescence characteristics as the average value of each sample.

[Example 3]
Example except that terbium oxide (Tb ₄ O ₇ , purity 99.99 mass%) was used as a starting material instead of praseodymium oxide (Pr ₆ O ₁₁ , purity 99.99 mass%) (Lm = Tb) In the same manner as in Example 1, a scintillator single crystal of Example 3 was produced. In addition, about the obtained single crystal ingot, the result of the segregation coefficient of Tb 0.7, the segregation coefficient of Ce 0.25, and the segregation coefficient of Ca 0.15 was obtained from the result of the elemental analysis. Further, the obtained single crystal for scintillator was measured for fluorescence characteristics in the same procedure as in Example 1. Table 1 shows the composition formula of this example and the measurement results of the fluorescence characteristics as the average value of each sample.

[Example 4]
Examples except that the amounts of lutetium oxide and cerium oxide as starting materials were adjusted so that x = 1.996 was x = 1.985 and y = 0.003 was y = 0.0005 In the same manner as in Example 3, a scintillator single crystal of Example 4 was produced. Further, the obtained single crystal for scintillator was measured for fluorescence characteristics in the same procedure as in Example 1. Table 1 shows the composition formula of this example and the measurement results of the fluorescence characteristics as the average value of each sample.

[Example 5]
Example except for using thulium oxide (Tm ₂ O ₃ , purity 99.99 mass%) instead of praseodymium oxide (Pr ₆ O ₁₁ , purity 99.99 mass%) as a starting material (Lm = Tm) In the same manner as in Example 1, a scintillator single crystal of Example 5 was produced. In addition, about the obtained single crystal ingot, the segregation coefficient of Tm was 0.8, the segregation coefficient of Ce was 0.26, and the segregation coefficient of Ca was 0.15 from the result of the elemental analysis. Further, the obtained single crystal for scintillator was measured for fluorescence characteristics in the same procedure as in Example 1. Table 1 shows the composition formula of this example and the measurement results of the fluorescence characteristics as the average value of each sample.

[Example 6]
Examples except that the amounts of lutetium oxide and cerium oxide as starting materials were adjusted so that x = 1.996 was x = 1.985 and y = 0.003 was y = 0.0005 In the same manner as in Example 5, a scintillator single crystal of Example 6 was produced. Further, the obtained single crystal for scintillator was measured for fluorescence characteristics in the same procedure as in Example 1. Table 1 shows the composition formula of this example and the measurement results of the fluorescence characteristics as the average value of each sample.

[Example 7]
Ln _{2− (x + y + z)} Lu _x Ce _y Lm _z SiO ₅ (Ln = Gd, Lm = Tb, x = 1.8, y = 0.003, z = 0.001) In the same manner as in Example 1 except that gadolinium oxide (Gd ₂ O ₃ , purity 99.99% by mass) and terbium oxide (Tb ₄ O ₇ , purity 99.99% by mass) were used as starting materials. A single crystal for scintillator of Example 7 was produced. Further, the obtained single crystal for scintillator was measured for fluorescence characteristics in the same procedure as in Example 1. Table 2 shows the composition formula of this example and the measurement results of the fluorescence characteristics as the average value of each sample.

[Example 8]
The scintillator single crystal of Example 8 was prepared in the same manner as in Example 7 except that the amounts of gadolinium oxide and cerium oxide as starting materials were adjusted so that y = 0.003 was changed to y = 0.0005. Produced. Further, the obtained single crystal for scintillator was measured for fluorescence characteristics in the same procedure as in Example 1. Table 2 shows the composition formula of this example and the measurement results of the fluorescence characteristics as the average value of each sample.

[Example 9]
Ln _{2− (x + y + z)} Lu _x Ce _y Lm _z SiO ₅ (Ln = Y, Lm = Tb, x = 1.8, y = 0.003, z = 0.001) In the same manner as in Example 1, except that yttrium oxide (Y ₂ O ₃ , purity 99.99 mass%) and terbium oxide (Tb ₄ O ₇ , purity 99.99 mass%) were used as starting materials. A scintillator single crystal of Example 9 was produced. Further, the obtained single crystal for scintillator was measured for fluorescence characteristics in the same procedure as in Example 1. Table 3 shows the composition formula of this example and the measurement results of the fluorescence characteristics as the average value of each sample.

[Example 10]
As a starting material, the scintillator single crystal of Example 10 was prepared in the same manner as in Example 9 except that the amounts of yttrium oxide and cerium oxide were adjusted so that y = 0.003 was changed to y = 0.0005. Produced. Further, the obtained single crystal for scintillator was measured for fluorescence characteristics in the same procedure as in Example 1. Table 3 shows the composition formula of this example and the measurement results of the fluorescence characteristics as the average value of each sample.

[Example 11]
Gd _{2− (a + x + y + z)} Ln _a Lu _x Ce _y Lm _z SiO ₅ (Ln = Y, Lm = Tb, a = 0.06, x = 1.86, y = 0.003, z = 0.001) As starting materials, gadolinium oxide (Gd ₂ O ₃ , purity 99.99% by mass), yttrium oxide (Y ₂ O ₃ , purity 99.99% by mass) and terbium oxide (Tb ₄ O) are used so as to have a stoichiometric composition. ₇ and a purity of 99.99 mass%) was used in the same manner as in Example 1 to produce a scintillator single crystal of Example 11. Further, the obtained single crystal for scintillator was measured for fluorescence characteristics in the same procedure as in Example 1. Table 4 shows the composition formula of this example and the measurement results of the fluorescence characteristics as the average value of each sample.

[Example 12]
The scintillator single crystal of Example 12 was prepared in the same manner as in Example 11 except that the amounts of gadolinium oxide and cerium oxide as starting materials were adjusted so that y = 0.003 was changed to y = 0.0005. Produced. Further, the obtained single crystal for scintillator was measured for fluorescence characteristics in the same procedure as in Example 1. Table 4 shows the composition formula of this example and the measurement results of the fluorescence characteristics as the average value of each sample.

[Comparative Example 1]
Comparison was made in the same manner as in Example 1 except that praseodymium oxide was not used as a starting material (z = 0), and the amount of lutetium oxide was adjusted so that x = 1.996 was changed to x = 1.997. A scintillator single crystal of Example 1 was produced. Further, the obtained single crystal for scintillator was measured for fluorescence characteristics in the same procedure as in Example 1. Table 1 shows the composition formula of this example and the measurement results of the fluorescence characteristics as the average value of each sample.

[Comparative Example 2]
Comparison was made in the same manner as in Example 2 except that praseodymium oxide was not used as a starting material (z = 0), and the amount of lutetium oxide was adjusted so that x = 1.985 was x = 1.9995. A scintillator single crystal of Example 2 was produced. Further, the obtained single crystal for scintillator was measured for fluorescence characteristics in the same procedure as in Example 1. Table 1 shows the composition formula of this example and the measurement results of the fluorescence characteristics as the average value of each sample.

[Comparative Example 3]
A scintillator single crystal of Comparative Example 3 was produced in the same manner as in Example 7 except that terbium oxide was not used as a starting material (z = 0) and the amount of gadolinium oxide was adjusted accordingly. Further, the obtained single crystal for scintillator was measured for fluorescence characteristics in the same procedure as in Example 1. Table 2 shows the composition formula of this example and the measurement results of the fluorescence characteristics as the average value of each sample.

[Comparative Example 4]
A scintillator single crystal of Comparative Example 4 was produced in the same manner as in Example 8 except that terbium oxide was not used as a starting material (z = 0) and the amount of gadolinium oxide was adjusted accordingly. Further, the obtained single crystal for scintillator was measured for fluorescence characteristics in the same procedure as in Example 1. Table 2 shows the composition formula of this example and the measurement results of the fluorescence characteristics as the average value of each sample.

[Comparative Example 5]
A scintillator single crystal of Comparative Example 5 was produced in the same manner as in Example 9 except that terbium oxide was not used as a starting material (z = 0) and the amount of yttrium oxide was adjusted accordingly. Further, the obtained single crystal for scintillator was measured for fluorescence characteristics in the same procedure as in Example 1. Table 3 shows the composition formula of this example and the measurement results of the fluorescence characteristics as the average value of each sample.

[Comparative Example 6]
A scintillator single crystal of Comparative Example 6 was produced in the same manner as in Example 10 except that terbium oxide was not used as a starting material (z = 0) and the amount of yttrium oxide was adjusted accordingly. Further, the obtained single crystal for scintillator was measured for fluorescence characteristics in the same procedure as in Example 1. Table 3 shows the composition formula of this example and the measurement results of the fluorescence characteristics as the average value of each sample.

[Comparative Example 7]
A scintillator single crystal of Comparative Example 7 was produced in the same manner as in Example 11 except that terbium oxide was not used as a starting material (z = 0) and the amount of gadolinium oxide was adjusted accordingly. Further, the obtained single crystal for scintillator was measured for fluorescence characteristics in the same procedure as in Example 1. Table 4 shows the composition formula of this example and the measurement results of the fluorescence characteristics as the average value of each sample.

[Comparative Example 8]
A scintillator single crystal of Comparative Example 8 was produced in the same manner as in Example 12 except that terbium oxide was not used as the starting material (z = 0) and the amount of gadolinium oxide was adjusted accordingly. Further, the obtained single crystal for scintillator was measured for fluorescence characteristics in the same procedure as in Example 1. Table 4 shows the composition formula of this example and the measurement results of the fluorescence characteristics as the average value of each sample.

[Comparative Example 9]
Example except that erbium oxide (Er ₂ O ₃ , purity 99.99 mass%) was used instead of praseodymium oxide (Pr ₆ O ₁₁ , purity 99.99 mass%) as a starting material (Lm = Er) In the same manner as in Example 1, a scintillator single crystal of Comparative Example 9 was produced. Further, the obtained single crystal for scintillator was measured for fluorescence characteristics in the same procedure as in Example 1. Table 1 shows the composition formula of this example and the measurement results of the fluorescence characteristics as the average value of each sample.

[Comparative Example 10]
Example except that erbium oxide (Er ₂ O ₃ , purity 99.99 mass%) was used instead of praseodymium oxide (Pr ₆ O ₁₁ , purity 99.99 mass%) as a starting material (Lm = Er) In the same manner as in Example 10, a scintillator single crystal of Comparative Example 10 was produced. Further, the obtained single crystal for scintillator was measured for fluorescence characteristics in the same procedure as in Example 1. Table 1 shows the composition formula of this example and the measurement results of the fluorescence characteristics as the average value of each sample.

  When Examples 1, 3, 5 and Comparative Example 1 are compared, it can be seen that Examples 1, 3, 5 have higher fluorescence output and better energy resolution than Comparative Example 1 (Table 1). That is, as compared with the case of activation of cerium alone, the fluorescence output and energy resolution are improved by co-activating the phosphor with cerium and at least one element selected from praseodymium, terbium, and thulium. The same applies when Examples 2, 4, and 6 are compared with Comparative Example 2 (Table 1). Even in the case of co-activation, the results of Comparative Examples 9 and 10 activated with erbium are inferior in fluorescence output and energy resolution due to the coloration of the crystals when compared with Comparative Examples 1 and 2, respectively.

  When Example 7 and Comparative Example 3 are compared, it can be seen that Example 7 has higher fluorescence output and better energy resolution (Table 2). When Example 8 and Comparative Example 4 are compared, it can be seen that Example 8 has higher fluorescence output and better energy resolution (Table 2). It can be said that not only LSO but also LGSO is based on LGSO by co-activating the phosphor with cerium and at least one element selected from praseodymium, terbium, and thulium.

  When Example 9 and Comparative Example 5 are compared, it can be seen that Example 9 has higher fluorescence output and better energy resolution (Table 3). When Example 10 and Comparative Example 6 are compared, it can be seen that Example 10 has higher fluorescence output and better energy resolution (Table 3). Even when the matrix structure is LYSO, it can be said that the fluorescence output and the energy resolution are improved by co-activating the phosphor with cerium and at least one element selected from praseodymium, terbium, and thulium.

  When Example 11 and Comparative Example 7 are compared, it can be seen that Example 11 has higher fluorescence output and better energy resolution (Table 4). When Example 12 and Comparative Example 8 are compared, it can be seen that Example 12 has higher fluorescence output and better energy resolution (Table 4). Even when the matrix structure is LGYSO, it can be said that the fluorescence output and the energy resolution are improved by co-activating the phosphor with cerium and at least one element selected from praseodymium, terbium, and thulium.

  Next, Table 5 shows the improvement rate of the fluorescence output by coactivation at the same cerium concentration (y value in the composition formula is equal). The fluorescence output ratio (%) was determined using the fluorescence output value (ch) of the example as the numerator and the fluorescence output value (ch) of the comparative example as the denominator.

  As is apparent from the results shown in Table 5, when y is 0.003 (cerium high concentration side), the average value is 103%, and when y is 0.0005 (cerium low concentration side), the average value is 108%. there were. That is, it can be said that the fluorescence output improvement by co-activation is larger at the cerium low concentration side.

  Further, when a combination is considered for DOI-PET use by co-activating the cerium low concentration side (y = 0.0005), the fluorescence output ratio (%) with the cerium low concentration side as the numerator and the cerium high concentration side as the denominator. ) Was determined and shown in Table 6.

  As is clear from the results shown in Table 6, the average value of both cerium low concentration side and high concentration side is 90% when cerium alone is used, and the average value is 97% when only the cerium low concentration side is co-activated. It was. That is, it can be said that the fluorescence output difference from the high concentration side can be greatly reduced by co-activating the cerium low concentration side.

  In addition, when both the cerium low concentration side (y = 0.0005) and the high concentration side (y = 0.003) are co-activated and considered as a DOI-PET application, the cerium low concentration side is a molecule. Fluorescence output ratio (%) was determined using the cerium high concentration side as the denominator and is shown in Table 7.

  As is apparent from the results shown in Table 7, when both cerium low concentration side and high concentration side are cerium alone, the average value is 90%, and when both cerium low concentration side and high concentration side are co-activated. The average value was 94%. That is, it can be said that the fluorescence output difference can be reduced by combining the coactivities.

  From the above results, when adding at least one selected from praseodymium, terbium and thulium to the single crystal of the cerium-activated orthosilicate compound and co-activating the phosphor with cerium, regardless of the cerium concentration, The fluorescence output and energy resolution are improved, and the difference in fluorescence characteristics due to the cerium concentration can be reduced. In particular, the scintillator that combines the co-activation on the low cerium concentration side with the single activation on the cerium high concentration side can further reduce the difference in fluorescence characteristics. Yes, it is highly expected as a DOI type next-generation high-performance PET application.

[Example 13]
As starting materials, the amount of gadolinium oxide and cerium oxide was adjusted so that y = 0.0005 was changed to y = 0.015, and in an air atmosphere after cutting out a 4 × 6 × 20 mm ³ sample A scintillator single crystal of Example 13 was produced in the same manner as in Comparative Example 4 except that the heat treatment step in the electric furnace was not performed. Further, the obtained single crystal for scintillator was measured for fluorescence characteristics in the same procedure as in Example 1. Table 8 shows the composition formula of this example and the measurement results of the fluorescence characteristics as the average value of each sample.

[Example 14]
As starting materials, the amount of gadolinium oxide and cerium oxide was adjusted so that y = 0.003 becomes y = 0.015, and in the air atmosphere after cutting out a 4 × 6 × 20 mm ³ sample A scintillator single crystal of Example 14 was produced in the same manner as Comparative Example 7 except that the heat treatment step in the electric furnace was not performed. Further, the obtained single crystal for scintillator was measured for fluorescence characteristics in the same procedure as in Example 1. Table 8 shows the composition formula of this example and the measurement results of the fluorescence characteristics as the average value of each sample.

[Example 15]
As starting materials, the amount of gadolinium oxide and cerium oxide was adjusted so that y = 0.003 becomes y = 0.015, and z = 0.001 was adjusted so that z = 0.004. The scintillator single crystal of Example 15 was obtained in the same manner as in Example 11 except that the heat treatment step in the electric furnace in the air atmosphere after cutting out the 4 × 6 × 20 mm ³ sample was not performed. Produced. Further, the obtained single crystal for scintillator was measured for fluorescence characteristics in the same procedure as in Example 1. Table 8 shows the composition formula of this example and the measurement results of the fluorescence characteristics as the average value of each sample.

  Moreover, the measurement result of the fluorescence characteristic of Example 1, the comparative examples 4 and 7 was combined with Table 8 as a comparison object of Examples 13-15, and was shown.

  In Example 13 and Example 14 of Table 8, the fluorescence characteristic of the composition (y = 0.015) whose cerium density | concentration is higher than the single crystal for scintillators of Examples 1-12 was measured with the activator of cerium alone. . The fluorescence decay time is about 46 ns. Considering each combination of Example 13 and Example 8, Example 14 and Example 12, the difference in fluorescence decay time is 10 ns or more. In Example 15, the fluorescence characteristics of a composition (y = 0.015) having a similarly high cerium concentration with a co-activator of terbium and cerium were measured. Similarly, the fluorescence decay time was about 46 ns, and the fluorescence output was improved. In the DOI-type next-generation high-performance PET, the difference in fluorescence decay time between the two types of scintillators to be combined is ideally 10 ns or more, and the cerium high-concentration side having the composition of Example 13, 14 or 15 and co-activated cerium In combination with the low concentration side (for example, Example 8 or 12 above), the difference in fluorescence output is further small and suitable for DOI type next-generation high-performance PET applications.

  For the single crystals of Examples 13, 14, 15 and 1, and Comparative Examples 4 and 7, UV-excited fluorescence spectra with ultraviolet light having an excitation wavelength of 364 nm are shown in FIG. In FIG. 2, A1 shows Example 13, B1 shows Example 14, C1 shows Example 15, D1 shows Example 1, E1 shows Comparative Example 4, and F1 shows Comparative Example 7. The fluorescence spectra in the single crystals of Examples 13 to 15 indicate the fluorescence with the maximum fluorescence output near the wavelength of 420 nm. In Example 13, Example 14, and Example 15 in which the cerium concentration is high (y = 0.015), the ratio of the fluorescence long wavelength component near 500 nm is increased in the fluorescence spectrum shown in FIG. I understand that. Due to this characteristic change, it is considered that excellent fluorescence characteristics are exhibited in combination with a semiconductor detector such as an avalanche photodiode having a maximum sensitivity wavelength of 500 nm or more.

DESCRIPTION OF SYMBOLS 1 ... Single crystal, 2 ... Seed crystal, 10 ... Lifting device, 12 ... Lifting rod, 13 ... Heater, 14 ... High frequency induction heating furnace, 15 ... High frequency induction coil, 16 ... Crucible support rod, 17 ... Crucible, 18 ... Melting Liquid (melt).

Claims (10)

A single crystal for a scintillator containing a cerium-activated orthosilicate compound represented by the following general formula (1).
_{Gd 2- (a + x + y} + z) Ln a Lu x Ce y Lm z SiO 5 ...... (1)
(In General Formula (1), Lm represents at least one element selected from Pr, Tb and Tm, Ln represents at least one element selected from Sc, Y, and a lanthanoid element excluding Pr, Tb and Tm. Represents an element, a represents a value of 0 or more and less than 1, x represents a value greater than 1 and less than 2, y represents a value greater than 0 and less than or equal to 0.01, and z is greater than 0 and less than or equal to 0.01 (The value of a + x + y + z is 2 or less.)   2. The scintillator single crystal according to claim 1, wherein Ln is Gd, a is greater than 0 and less than 1, and Lm is at least one element selected from Tb and Tm.   2. The scintillator single crystal according to claim 1, wherein Ln is Y, and a is greater than 0 and less than 1. 3.   2. The scintillator single crystal according to claim 1, wherein Ln is Y, a is greater than 0 and less than or equal to 0.2, and x is greater than 1.6 and less than 2. 3.   5. The composition according to claim 1, comprising 0.00005 to 0.1% by mass of at least one additive element selected from elements belonging to Group 2 (Group IIa) of the periodic table based on the total mass of the single crystal. The single crystal for scintillators according to claim 1.   6. The composition according to claim 1, comprising 0.00005 to 0.1 mass% of at least one additive element selected from elements belonging to Group 13 (Group IIIb) of the periodic table based on the total mass of the single crystal. The single crystal for scintillators according to claim 1. A heat treatment method for producing the scintillator single crystal according to any one of claims 1 to 6,
A single crystal grown using a raw material containing a constituent element of a single crystal for scintillator containing a cerium-activated orthosilicate compound represented by the following general formula (1) is 700 to 1500 ° C. in an oxygen-containing atmosphere. The heat processing method which heat-processes at the temperature of.
_{Gd 2- (a + x + y} + z) Ln a Lu x Ce y Lm z SiO 5 ...... (1)
(In General Formula (1), Lm represents at least one element selected from Pr, Tb and Tm, Ln represents at least one element selected from Sc, Y, and a lanthanoid element excluding Pr, Tb and Tm. Represents an element, a represents a value of 0 or more and less than 1, x represents a value greater than 1 and less than 2, y represents a value greater than 0 and less than or equal to 0.01, and z is greater than 0 and less than or equal to 0.01 (The value of a + x + y + z is 2 or less.) A method for producing a scintillator single crystal according to any one of claims 1 to 6,
Preparing a raw material containing a constituent element of a scintillator single crystal containing a cerium activated orthosilicate compound represented by the following general formula (1), and growing a single crystal by the Czochralski method;
And a step of heat-treating the single crystal body at a temperature of 700 to 1500 ° C. in an oxygen-containing atmosphere.
_{Gd 2- (a + x + y} + z) Ln a Lu x Ce y Lm z SiO 5 ...... (1)
(In General Formula (1), Lm represents at least one element selected from Pr, Tb and Tm, Ln represents at least one element selected from Sc, Y, and a lanthanoid element excluding Pr, Tb and Tm. Represents an element, a represents a value of 0 or more and less than 1, x represents a value greater than 1 and less than 2, y represents a value greater than 0 and less than or equal to 0.01, and z is greater than 0 and less than or equal to 0.01 (The value of a + x + y + z is 2 or less.) A scintillator single crystal comprising a cerium-activated orthosilicate compound represented by the following general formula (2), wherein at least one additive element selected from elements belonging to Group 2 (Group IIa) of the periodic table, The ratio of the fluorescence intensity at the excitation wavelength of 364 nm to the fluorescence intensity at the excitation wavelength of 304 nm (364 nm / 304 nm) is less than 3 at 0.00005 to 0.1% by mass based on the total mass of the single crystal. A single crystal for scintillator.
_{Gd 2- (a + x + y} + z) Ln a Lu x Ce y Lm z SiO 5 ...... (2)
(In general formula (2), Lm represents at least one element selected from Pr, Tb and Tm, Ln represents at least one element selected from Sc, Y, and a lanthanoid element excluding Pr, Tb and Tm. Represents an element, a represents a value of 0 or more and less than 1, x represents a value of more than 1 and less than 2, y represents a value of more than 0.01 and 0.03 or less, and z is 0 or more and 0.01 (The following values are shown, where a + x + y + z is 2 or less.) A method for producing a scintillator single crystal according to claim 9,
A scintillator comprising a step of preparing a raw material containing a constituent element of a single crystal for scintillator containing a cerium activated orthosilicate compound represented by the following general formula (2), and growing a single crystal by the Czochralski method For producing a single crystal for use.
_{Gd 2- (a + x + y} + z) Ln a Lu x Ce y Lm z SiO 5 ...... (2)
(In general formula (2), Lm represents at least one element selected from Pr, Tb and Tm, Ln represents at least one element selected from Sc, Y, and a lanthanoid element excluding Pr, Tb and Tm. Represents an element, a represents a value of 0 or more and less than 1, x represents a value of more than 1 and less than 2, y represents a value of more than 0.01 and 0.03 or less, and z is 0 or more and 0.01 (The following values are shown, where a + x + y + z is 2 or less.)

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